1. Field of the Invention
The present invention relates to a method for producing multi-layered chip inductors, in which a large number of external electrodes can be readily formed.
2. Description of the Related Art
A conventional method for producing chip inductors will be explained with reference to FIGS. 10 to 12.
First, a slurry of a magnetic ceramic material is applied to the surface of a base film, dried, and then stripped from the base film to obtain a magnetic green sheet (not shown in the figures). In the ceramic arts, the term xe2x80x9cgreenxe2x80x9d generally refers to a ceramic part in its unsintered state, as explained on pages 181-185 of Engineering Materials Handbook: Ceramics and Glasses, Vol. 4, 1991, ASM International. Green sheet pieces 1b having a predetermined size are then prepared by cutting the magnetic green sheet. A via hole 2 is made at a predetermined position on each of the green sheet pieces 1b. A coil-shaped internal conductor pattern 3 is printed, for example, using a paste essentially consisting of Ag, at a predetermined position on each of the green sheet pieces 1b. A predetermined number of the green sheet pieces 1b are laminated to form a coil spiralled in the laminating direction, as is shown in FIG. 10. Electrical continuity between the printed coil-shaped internal conductor patterns 3 of the green sheet pieces 1b is achieved through the via holes 2, as is shown by the dotted lines in FIG. 10. A predetermined number of green sheet pieces 1a on which no conductor pattern is printed are provided above and below the laminated green sheet pieces 1b and are pressed to adhere to one another and to adhere to the green sheet pieces 1b.
In a practical manufacturing process, large-area green sheet pieces having a plurality of coil-shaped internal conductors are used for preparing a green ceramic laminate 4 comprising a group of chip-shaped laminates, shown in FIG. 11. The green ceramic laminate 4 is cut along the dotted lines 5 and 6 to obtain chip-shaped green ceramic laminates 7 having a structure shown in FIG. 12. Each end 3a of the coil-shaped internal conductors 103 formed inside the chip-shaped green ceramic laminates 7 is exposed on the corresponding cut face.
Each of the chip-shaped green ceramic laminates 7 is then fired. To obtain a multi-layered chip inductor, external-electrode-paste layers 8 are formed on the cut faces, which are parallel to the lamination direction of the fired chip-shaped ceramic laminate 7 so that the external-electrode-paste layers 8 electrically connect to the corresponding ends 3a of the coil-shaped internal conductor 103, as is shown in FIG. 12.
However, according to the above structure, the ends 3a of the coil-shaped internal conductor 103 are located inside the green ceramic laminate 4, i.e., exposed on the cut faces of each chip-shaped laminate 7. Therefore, for producing a multi-layered chip inductor having the above structure, the following procedure is required: the green ceramic laminate 4 is cut into chip-shaped laminates 7 so that each end 3a of coil-shaped internal conductors 103 is exposed on a cut face; and the external-electrode-paste layers 8 are formed on the cut faces having the exposed ends 3a at chip-shaped laminates 7.
Thus, disadvantageously, a jig, an extra manufacturing step, and longer processing time are required for forming the external-electrode-paste layers 8 on the corresponding cut faces of each chip-shaped laminate 7.
To solve the above problems, the present invention is aimed at providing a method for producing a multi-layered chip inductor, in which a large number of external electrodes can be readily formed by applying an external electrode paste to the laminating-direction surfaces of a ceramic laminate that has not yet been cut into chip-shaped laminates. In the following discussion, the term xe2x80x9claminating-direction surfacexe2x80x9d pertains to a direction parallel to the surfaces of the laminated sheets. The term xe2x80x9claminating directionxe2x80x9d pertains to a direction generally perpendicular to the surface of the laminated sheets, which also generally corresponds to the longitudinal axis of an inductor coil within the multi-layered chip inductor.
According to the present invention, a method for producing a multi-layered chip inductor comprises: a step for forming coil-shaped internal conductors inside a green ceramic laminate, each of which coil-shaped internal conductors is spiralled around an axial line in the laminating direction of the green ceramic laminate; a step for applying an external electrode paste onto at least one laminating-direction surface of the green ceramic laminate, which external electrode paste electrically connects to an end of the coil-shaped internal conductors; a step for cutting the green ceramic laminate along the laminating direction into chip-shaped green ceramic laminates each having a coil-shaped internal conductor inside; and a step for firing each of the chip-shaped green ceramic laminates and baking the external electrode paste to form an external electrode.
In addition, another method for producing a multi-layered chip inductor comprises: a step for forming coil-shaped internal conductors inside a green ceramic laminate, each of which coil-shaped internal conductors is spiralled around an axial line in the laminating direction of the green ceramic laminate; a step for applying an external electrode paste onto at least one laminating-direction surface of the green ceramic laminate, which external electrode paste electrically connects to an end of the coil-shaped internal conductors; a step for firing the green ceramic laminate and baking the external electrode paste to form an external electrode; and a step for cutting the fired ceramic laminate along the laminating direction into chip-shaped ceramic laminates each having a coil-shaped internal conductor inside.
Still another method for producing a multi-layered chip inductor comprises: a step for forming coil-shaped internal conductors inside a green ceramic laminate, each of which coil-shaped internal conductors is spiralled around an axial line in the laminating direction of the green ceramic laminate; a step for firing the green ceramic laminate; a step for applying and baking an external electrode paste electrically connected to an end of the coil-shaped internal conductors onto at least one laminating-direction surface of the fired ceramic laminate so as to form an external electrode; and a step for cutting the fired ceramic laminate, on which the external electrode paste has been baked to form an external electrode, along the laminating direction into chip-shaped ceramic laminates each having a coil-shaped internal conductor inside.
Furthermore, for each chip inductor, both ends of the coil-shaped internal conductor are led to one laminating-direction surface of the multi-layered chip inductor and two baked external electrodes are formed on this laminating-direction surface so that the electrodes are electrically connected to the corresponding ends. Preferably, a plating layer is formed on the surface of the baked external electrode.
Another method for producing a multi-layered chip inductor comprises: a step for forming coil-shaped internal conductors inside a green ceramic laminate, each of which coil-shaped internal conductors is spiralled around an axial line in the laminating direction of the green ceramic laminate; a step for firing the green ceramic laminate and forming an external thin-film electrode on at least one laminating-direction surface of the fired ceramic laminate, which external thin-film electrode electrically connects to an end of the coil-shaped internal conductors; and a step for cutting the fired ceramic laminate along the laminating direction into chip-shaped ceramic laminates each having a coil-shaped internal conductor inside.
Both ends of the coil-shaped internal conductor are led to one laminating-direction surface of the multi-layered chip inductor and two baked external thin-film electrodes are formed on this one laminating-direction surface so that the electrodes are electrically connected to the corresponding ends of the coil-shaped internal conductor. Preferably, a plating layer is formed on the surface of said external thin-film electrodes.
According to the above methods, external electrodes can be provided on a laminating-direction surface of a ceramic laminate (i.e., a group of chip-shaped laminates) which has not yet been divided into chip-shaped laminates.
The invention also pertains to multi-layered chip inductors produced by the aforementioned methods.